How do I get varnish to return in the http response header from which backend it took the response?

I have three servers in the backend, with a round robin director.

I would like varnish to write a X-Server-By header with the name or ip of the server from which the response was fetched, how can this be done?

From serverfault $pageUsers[$entry.posts[0].author].name

• The following is not tested, but might get you started:

  sub vcl_deliver {
      set resp.http.X-Served-By = server.hostname;
      deliver;
  }
  

  From Conor McDermottroe

• sub vcl_fetch {
      set obj.http.X-Backend = req.backend;
  }
  

  Tested on 2.0.6 in my (non round robin) setup. It should give you something to go on.

  From rossnz